Hard copy devices process images on media, typically taking the form of printers, plotters (employing inkjet or electron photography imaging technology), scanners, facsimile machines, laminating devices, and various combinations thereof, to name a few. These hard copy devices typically transport media in a sheet form from a supply of cut sheets or a roll, to an interaction zone where printing, scanning or post-print processing, such as laminating, overcoating or folding occurs. Often different types of media are supplied from different supply sources, such as those containing plain paper, letterhead, transparencies, pre-printed media, etc.
In some kinds of hard copy apparatus a vacuum apparatus is used to apply a suction or vacuum force to a sheet of flexible media to adhere the sheet to a surface, or to stabilize the sheet relative to the surface, for example, for holding a sheet of print media temporarily to a platen. Such vacuum holddown systems are an economical technology to implement commercially and can improve machine throughput specifications and the quality of the print job. There are a variety of vacuum platen systems.
As wet ink is deposited onto media the surface of the media may be distorted. This distortion of the media that results from interactions between the wet ink and the media, can impact the ability of vacuum holddown systems to reliably stabilize the media, and can likewise have an adverse impact on print quality.
A holddown for a hard copy device comprises a member having a surface and plural vacuum zones. Each of the vacuum zones defines a cavity in the surface having at least one port therethrough, and each cavity is defined by a sidewall circumscribing the cavity. At least one of the cavities has sidewall with a first section at a first height relative to the surface and a second section at a second height relative to the surface.